1. Field of the Invention
The present invention relates to an ultrasonic gas meter with a housing having an inlet and an outlet, a partition wall arranged between the inlet and the outlet and dividing the housing, a measuring tube passing through the partition wall and having an inlet aperture on one end and an outlet aperture on the other end wall, ultrasonic transducers disposed on the inlet side upstream of the measuring tube and on the outlet side downstream of the measuring tube and at least one guidance duct running along the measuring tube, said guidance duct being connected on the inlet side with the housing inlet and on the outlet side with the inlet aperture of the measuring tube.
The two transducers function as both emitters and detectors. The volume of gas flowing through the meter is determined by measuring the time of flight of ultrasonic signals transmitted and received in both directions.
2. Prior Art
With a known flowmeter of the afore-mentioned type (EP 0479434 A1) the measuring tube is circular in cross-section and arranged centrally in the guidance duct. The transducers on the end walls are disposed in chambers which are sealed on all sides and which only have an aperture screened by a mesh in the wall adjacent to the measuring tube. The object of this design is to achieve a coupling of the substantially plane waves in the measuring tube.
However, the chambers lead to considerable losses of sound energy. This in turn leads to a reduction in measuring accuracy. Moreover, the known design is complicated. In particular, the chambers have to be lined with sound-absorbing material. Further, a space-saving design is not possible.